Infrared sensors, focal plane arrays and thermal imaging systems

ABSTRACT

An infrared sensor and infrared imaging system, wherein said infrared sensor comprises: a first film structure, a second film structure, a gap between said first film structure and said second film structure. Reference light is incident from one of said first film structure and said second film structure. When said gap distance changes, the intensity of transmitted reference light changes, and the intensity of reflected reference light changes. When infrared light is incident, at least one of the said first and second film structures absorbs infrared light and the temperature changes, causing said gap distance to change. By detecting the intensity of said transmitted reference light or reflected reference light, the incident infrared light can be measured.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/681,186, filed Mar. 25, 2010, now allowed, which is a U.S. NationalStage of International Application No. PCT/CN2007/002845 filed Sep. 28,2007. The contents of these applications are incorporated herein byreference in their entirety.

TECHNICAL FIELDS

This invention relates to infrared sensors, focal plane arrays andthermal imaging systems, especially infrared sensors, focal plane arraysand thermal imaging systems for detecting infrared lights emitted byobjects.

TECHNICAL BACKGROUND

Infrared sensors detect infrared emission from objects at wavelengthbetween about 8 μm to 14 μm that are not visible to human eyes, CCD orCMOS cameras. Traditional infrared sensors are fabricated using narrowband gap semiconductors or microbolometers, and they are difficult tomake and expensive. Currently, there are some technologies that convertinfrared signals into visible signals, and obtain the infrared image bycalculating the infrared signal from the detected visible signals. Onetechnology uses Micro-Electro-Mechanical Systems (MEMS) technology tomanufacture infrared sensor array, i.e., focal plane array (FPA). Inthese structures, the supporting beams are made of different materialshaving different coefficients of thermal expansion (CTE), and when theabsorbing plate absorbs incident infrared light, and transmits theabsorbed heat to the supporting beams, the temperature of the supportingbeams rises, and the supporting beams and the absorbing plate (also actsas a reflecting plate) bend, causing the reflected visible light todeflect. The intensity of the incident infrared light can be calculatedby detecting the deflection angle of the visible light. This methodmeasures the deflection of the visible lights, and involves complicatedreadout optical setup. Its manufacturing process is also difficult tocontrol.

There are other technologies that convert infrared signals into visiblesignals, such as described by CN1427251A. The technology uses opticalcrystal which is difficult for production. The optical setup is alsocomplicated, and the detected infrared light is from active infraredillumination, not infrared light emitted from objects.

Therefore, a simple, efficient, sensitive and accurate infrared sensoris needed for detecting infrared lights emitted by objects.

This invention provides a novel infrared sensor, focal plane array, andinfrared imaging system for detecting infrared emissions from objects.This invention overcomes the disadvantages of existing technologies, andcan accurately and speedily detect infrared emissions from objects, andconvert the infrared emissions to images.

In accordance with one aspect of this invention, it is provided aninfrared sensor that detects infrared emission from objects, whereinsaid infrared sensor comprises a first film structure, a second filmstructure, and a gap between said first film structure and said secondfilm structure. When a reference light is incident on one of said firstfilm structure and said second film structures, it is partiallyreflected and partially transmitted through the other film structure.When said gap between said two film structures changes, the intensity ofthe reflected reference light changes, as well as the intensity of thetransmitted reference light. When an infrared light is incident, atleast one of said first film structure and said second film structureabsorbs incident infrared light, changes its temperature, and causes thegap to change consequently. By detecting the changes in the intensity ofthe reflected or transmitted reference light, the incident infraredlight can be measured.

In accordance with another aspect of this invention, said infraredsensor further comprises a substrate, one or more first supportingmechanisms that support said first film structure on said substrate,wherein said second film structure is located directly on saidsubstrate.

In accordance with another aspect of this invention, said infraredsensor comprises a substrate, one or more first supporting mechanismsthat support said first film structure on said substrate; and one ormore second supporting mechanisms that support said second filmstructures on said substrate.

In accordance with another aspect of this invention, said firstsupporting mechanism or said second supporting mechanism has the samelayer structures as said first film structure or second film structurethat it supports.

In accordance with another aspect of this invention, said second filmstructure and said substrate is an integrated structure.

In accordance with another aspect of this invention, part of saidsubstrate is etched away to form an empty space. Said reference light isincident from the empty space and incident on said first film structureand said second film structure or incident on said first film structureand said second film structure and passes through said empty space.Infrared light is incident from the empty side or, from the oppositedirection, incident to said first film structure or said second filmstructure.

In accordance with another aspect of this invention, to increase theabsorption of the infrared light by the sensor, one of said first filmstructure and second film structure that is away from the incidentinfrared light is an infrared reflective film, or consists of aninfrared reflective film on the upper surface, lower surface orsomewhere in the middle. The infrared reflective film as described inthis invention is film made of materials that have strong reflectivityfor infrared emissions, including all conductive materials, such asmetal and transparent conductive material such as ITO. In accordancewith another aspect of this invention, transparent conductive materialssuch as ITO, InZnO and ZnO are used to make the infrared reflective filmin the transmission mode.

In accordance with another aspect of this invention, in order toincrease infrared absorption by the sensor, one of said first filmstructure and said second film structure that is on the incidentinfrared light side is an infrared absorbing film, or consists of aninfrared absorbing film on the upper surface, lower surface, orsomewhere in the middle. The infrared absorbing film as described inthis invention is film made of materials that have strong absorption forinfrared emissions at wavelength between 8 μm to 14 μm, includingmaterials that have absorption peak for infrared lights at wavelengthbetween 8 μm to 14 μm.

In accordance with another aspect of this invention, said firstsupporting mechanism of the sensor comprises a beam having one endattached to said first film structure and another end attached to saidsubstrate, said second film structure, or said second supportingmechanism; an additional layer attached with said beam. Said secondsupporting mechanism comprises a beam having one end attached to saidsecond film structure and another end attached to said substrate; anadditional layer attached with said beam. Said beam consists of amaterial or material combination with a first CTE, said additionallayers consist of a material or material combination with a second CTE.Said first CTE is different from said second CTE. Said first and secondsupporting mechanisms include straight beams, spin-wheel structures, andsymmetric structures.

In accordance with another aspect of this invention, part of said beamhas additional layer on the upper surface, and part of said beam hasadditional layer on the lower surface.

In accordance with another aspect of this invention, said first or saidsecond mechanism is a microbridge that supports said first filmstructure or the second film structure. Said microbridge has at leasttwo beams. Said beams may not have an additional layer.

In accordance with another aspect of this invention, in said infraredsensor, said first and second supporting mechanisms bend in the samedirection when the environment temperature changes so as to keep the gapbetween said two film structures unchanged. Said environment temperatureas described in this invention is the temperature of the environment inwhich the infrared sensor is located, not the temperature of the objectsthat the sensor detects.

In accordance with another aspect of this invention, said first filmstructure and said second film structure are reflective mirrorsrespectively, creating interference between said first film structureand said second film structure.

In accordance with another aspect of this invention, said first filmstructure and said second film structure consist of multiple layers ofmaterials. Said multiple layers of materials include symmetricstructure, wherein the types of materials are vertically symmetric whilethe thickness of layers may or may not be symmetric, such as 100 nmSiNx/100 nm SiO2/200 nm a-Si/120 nm SiO2/80 nm SiNx.

In accordance with another aspect of this invention, said first filmstructure, said second film structure consist of a single layer ormultiple layers of materials. Said single layer or multiple layers ofmaterials include silicon oxide (SiO2), silicon nitride (SiNx) oramorphous silicon (a-Si).

In accordance with another aspect of this invention, said first filmstructure and said second film structure consist of multiple layers ofmaterials. Said multiple layers of materials include 5 layers ofsymmetric materials: a-Si/SiO2/a-Si/SiO2/a-Si, orSiNx/SiO2/a-Si/SiO2/SiNx.

In accordance with another aspect of this invention, said first filmstructure and said second film structure consist of a single layer ormultiple layers of materials. The thickness of each layer in said singlelayer or multiple layers of materials is quarter wavelength of thereference light in the material.

In accordance with another aspect of this invention, said firstsupporting mechanism or second supporting mechanism includes: one ormore beams consist of one or more materials with a first CTE; multipleadditional layers attached to said beams, wherein said additional layersconsist of one or more materials with a second CTE; wherein saidadditional layers are arranged such that: when the environmenttemperature changes, said first supporting mechanism or said secondsupporting mechanism bend in such a way that the displacements canceleach other and the gap keeps unchanged. When there is incident infraredlight, the temperature of at least one of said first film structure andsaid second film structure rises, causing said first supportingmechanism or said second supporting mechanism to bend, the combinationof all the bending results in a change in said gap distance.

In accordance with another aspect of this invention, said first orsecond supporting mechanism consists of three sections: a first sectionthat is close to the substrate or has good thermal contact with thesubstrate, a second section that is close to said film structure that issupported by said supporting mechanism or has good thermal contact withsaid film structure, and a third section that is thermally insulatingand located between the above two sections. In accordance with anotheraspect of this invention, in said first or second supporting mechanism,said first section that is close to the substrate or has good thermalcontact with the substrate and second section that is close to said filmstructure that is supported by said supporting mechanism or has goodthermal contact with said film structure bend in opposite directionswhen the temperature changes.

In accordance with another aspect of this invention, said first orsecond supporting mechanism contains first additional layer or layersand second additional layer or layers, wherein said first additionallayer or layers and second additional layer or layers has two sections.Said total four sections are arranged as following: first section offirst additional layer or layers, second section of first additionallayer or layers, first section of second additional layer or layers, andsecond section of second additional layer or layers are sequentiallyattached to the beam, wherein first section of first additional layer orlayers and second section of second additional layer or layers areattached to the same side of the beam; said second section of said firstadditional layer or layers and said first section of the secondadditional layer or layers are attached to the same other side of thebeam.

In accordance with another aspect of this invention, at least one filmstructure in said first film structure and said second film structureabsorbs light at wavelength outside of the infrared light spectrum, andthe sensor is used to detect lights at such wavelength.

In accordance with another aspect of this invention, said substratecontains other devices or circuits, such as CMOS or CCD imaging devicesor circuits.

In accordance with another aspect of this invention, when said infraredsensor operates at transmission mode, said infrared reflective film istransparent to said reference light. When said infrared sensor operatesat reflectance mode, said infrared reflective film structure istransparent to said reference light or is metal.

In accordance with another aspect of this invention, a blind pixel isprovided to sense the environment temperature of the sensor. Said blindpixel comprises a substrate, a first film structure, a second filmstructure, a gap between said first film structure and said second filmstructure. Reference light is incident on one of said first filmstructure and said second film structure, and transmits from the otherfilm structure. When said gap changes, the intensity of said reflectedreference light or said transmitted reference light changes. At leastone of said first film structure and said second film structure absorbsinfrared light and has good thermal contact with said substrate. Wheninfrared light is incident on said first film structure and said secondfilm structure, said gap between said first film structure and saidsecond film structure does not change. When environment temperaturechanges, said gap distance changes. By detecting change in the intensityof said transmitted reference light from said second film structure, theenvironment temperature of the device is measured. Furthermore, thesupporting mechanism of said blind pixel has high thermal conductivity,or has a large width, thickness or cross section area, or has multiplebeams that increase the thermal conductivity between said first filmstructure or said second film structure and said substrate.

In accordance with another aspect of this invention, the film structurebetween said first film structure and said second film structure of saidblind pixel that is at the same side of the incident infrared light isan infrared reflective film, or contains an infrared reflective film onthe upper surface, lower surface, or somewhere in the middle.

Another blind pixel comprises: a substrate, a first film structureattached to the substrate, a medium attached to the first filmstructure, and a second film structure attached to the medium, whereinsaid first film structure, medium and second film structure forms aninterferometer. When infrared light is incident on said first filmstructure and said second film structure, the refractive index of saidmedium does not change. When environment temperature changes, therefractive index of said medium changes, causing the intensities of thetransmitted reference light and the reflected reference light from saidfirst film structure and said second film structure to change. Bydetecting the change in the intensity of said transmitted referencelight from said second film structure or said reflected reference light,the environment temperature of the device is measured.

In accordance with another aspect of this invention, said interferometeris connected to the substrate by a supporting mechanism, and has goodthermal contact with the substrate.

In accordance with another aspect of this invention, said interferometercontains infrared reflective film on the upper surface, lower surface,or somewhere in the middle.

In accordance with another aspect of this invention, a focal plane arrayis provided that contains one or more of the infrared sensors of thisinvention. Furthermore, another focal plane array is provided thatcontains one or more of the blind pixels provided in this invention.

In accordance with another aspect of this invention, an infrared imagingsystem is provided that contains: a reference light source, a focalplane array in accordance with this invention, a detector for detectingthe intensity of the reference light. The reference light source can bea LED; the detector can be a CCD or CMOS imaging chip.

This invention utilizes the principle of optical interference and hashigh sensitivity. Directly detecting the intensity of transmitted orreflected light, not deflection, is easy to implement. This inventionuses the gap as a resonance cavity. The suspending reflecting layer isjust a reflective film structure and has low thermal capacity. As aresult, the sensor has fast response time. The gap changes sensitivelywhen the temperature changes, and the sensor has high temperatureresolution.

ILLUSTRATION OF THE DRAWINGS

The following figures are used to illustrate the preferred embodimentsof this invention, as well as the purpose, characteristics andadvantages of this invention.

FIG. 1A-C shows an infrared sensor according to one embodiment of thisinvention.

FIG. 1D-F shows infrared sensors according to other embodiments.

FIG. 1G shows the spectrum of the infrared sensor and the referencelight according to one embodiment of this invention.

FIG. 1H shows the spectrum of the infrared sensor according to anotherembodiment.

FIG. 2A-C shows the spinwheel structure beams of the infrared sensoraccording to one embodiment.

FIG. 3A-C shows the single beam structure according to anotherembodiment.

FIG. 4A-B shows two reflexed beam structures according to anotherembodiment.

FIG. 5A-B shows the top view and cross-section of a microbridgestructure according to one embodiment.

FIG. 6A-D shows various positions of the infrared reflective filmstructure in the infrared sensor for enhancing infrared reflectingaccording to one embodiment.

FIG. 7A-C shows the beam structure used for temperature compensationaccording to one embodiment. The dashed line illustrates the bending ofthe beam as temperature changes.

FIG. 8 shows a structure with a first suspending reflective filmstructure and a second suspending reflective film structure used fortemperature compensation according to another embodiment.

FIG. 9A-C shows the structure of blind pixels according to oneembodiment of the invention.

SPECIFIC EMBODIMENTS

Various embodiments of the invention will be described in accordancewith the following drawings.

FIGS. 1A-C shows one embodiment of an infrared sensor described in thisinvention. As shown in FIGS. 1A-C, the infrared sensor comprises asubstrate (101), a reflective layer (103) that is above the substrate orsuspended above the substrate, a suspended reflective layer (104) thatis above the reflective layer (103) and forms a gap between thesuspending reflective layer (104) and the reflective layer (103), and abeam (106) which supports the reflective layer (104) over the substrate(101). Alternatively, beam (106) supports the reflective layer (104)over the reflective layer (103), as shown in FIG. 5B. In FIGS. 1A-C, thesubstrate (101) can be silicon or other semiconductor materials. If theinfrared sensor operates at transmission mode, the substrate (101) needsto be transparent to the incident reference light (102). Preferably,substrate (101) can be glass, other transparent materials, ornon-transparent materials with the materials etched away at where thereference light needs to pass.

The lower reflective layer (103) is attached on the substrate (101). Itoften comprises layers of two alternative materials with differentrefractive indices. The thickness of each layer is quarter wavelength ofthe reference light in the material, i.e., vacuum wavelength divided bythe refractive index. Such a structure forms a Brag reflector and hashigh reflectivity to the reference light. The reflective layer (103) cancomprise materials such as SiO2 and a-Si. Preferably, the reflectivelayer (103) is a symmetric 5 layer structure: a-Si/SiO₂/a-Si/SiO₂/a-Si,the thickness of each layer is quarter wavelength of the reference lightin the material.

The structure of the suspended reflective (104) is similar to that ofreflective layer (103). The suspended reflective layer (104), reflectivelayer (103) and the gap (105) between the two layers form a Fabry-Perotinterferometer. The suspended reflective layer (104) often compriseslayers of two or more materials with different refractive indices. Thethickness of each layer is quarter wavelength of the reference light inthe material. The reflective layer (104) can comprise materials such asSiO2 and a-Si. The suspended reflective layer (104) often comprises amaterial that has high absorption co-efficiency at the infraredwavelength, called infrared absorbing materials in this invention. Thefilm that consists of infrared absorbing material(s) is called infraredabsorbing film. Materials that have an absorption peak betweenwavelength 8 um to 14 um is called infrared absorbing materials. Oneexample is silicon nitride (SiNx), which has an absorption peak around11.4 um. Preferably, the suspending reflective layer (104) is a 5 layerstructure: SiNx/SiO₂/a-Si/SiO₂/SiNx.

The interferometer formed by the suspending reflective layer (104), thereflective layer (103) and the gap (105) selectively passes light atcertain wavelength. The transmitted light is the reference light in thisembodiment of the invention. The suspending reflective layer (104) andthe reflective layer (103) can be reflective mirrors, respectively.There might be one or more beams (106). Each beam (106) is connected tothe substrate (101) or the reflective layer (103) at one end, and isconnected to the suspending reflective layer (104) at the other end. Thebeam supports the suspending reflective layer (104), and is also athermal insulator. The smaller the cross-section, the longer the beamand the less the thermal conductivity, the better is the thermalinsulation.

In this embodiment of the invention, an additional layer (107) isattached to the beam (106). The CTE of the additional layer (107) isdifferent from that of the beam (106). Preferably, the CTE of theadditional layer (107) is larger than that of the beam (106). Forexample, the CTE of the additional layer (107) is larger than that ofthe beam (106) by 50%, or smaller by 35%. Preferably, the additionallayer (107) is a metal layer and the beam (106) is a non-metal layer.

Because the beam is thermally insulating, when the suspending reflectivelayer (104) absorbs infrared light, and its temperature rises, the heatis not immediately conducted to the substrate, but raise the temperatureof the beam (106) and the additional layer (107). Thus, it creates atemperature gradient between suspending reflective layer (104) and thesubstrate. As a result, when the temperature of the suspendingreflective layer (104) rises because of the incident infrared light, thetemperatures of the beam (106) and the additional layer (107) also rise,causing thermal expansion. Due to the different CTE's of the differentmaterials, the beam (106) bends upwards or downwards.

The beams (106) are arranged symmetrically across the structure as shownin FIG. 1B. Therefore, the suspending reflective layer (104) movesparallel to the substrate (101), causing the gap between the suspendingreflective layer (104) and reflective layer (103) to change, as well asthe resonant wavelength of the FP interferometer formed by suspendingreflective layer (104), reflective layer (103) and the gap. As a result,the intensities of the transmitted or reflected reference light change.By measuring the change in the intensity of the transmitted or reflectedreference light, the displacement of suspending reflective layer (104)can be calculated. Subsequently, the intensity of the incident infraredlight (108) can be calculated.

An alternative structure of the infrared sensor is illustrated in FIG.1D. This infrared sensor does not include a reflective layer. It onlycomprises: a substrate (101), a suspending reflective layer (104) thatsuspends above the substrate (101), a gap formed by the suspendingreflective layer (104) and the substrate (101), and a beam (106) thatsupports the layer (104) over the substrate (101). In this alternativeconfiguration, the substrate (101), the layer (104) and the gap formsthe interferometer. Similar to the above embodiment, when the suspendingreflective layer (104) absorbs incident infrared light and itstemperature rises, it causes the gap to change. By measuring the changein the intensity of the transmitted or reflected reference light, theintensity of the incident infrared light (108) can be calculated.

The infrared sensors in accordance with this invention can have manydifferent structures. FIG. 1D-F shows some of the alternativestructures. In FIG. 1D, the infrared sensor comprises a suspendingreflective layer (104), a substrate (101), and a beam (106). In thisalternative configuration, the substrate (101) functions as a reflectivelayer, or the substrate is integrated with the reflective layer. Whenthe infrared light (108) is incident on the suspending reflective layer(104), the temperature of suspending reflective layer (104) rises andthe gap between suspending reflective layer (104) and substrate (101)changes. As a result, the intensity of the transmitted or reflectedreference light changes and the intensity of the infrared light can becalculated. In FIG. 1E, the substrate (101) is above the suspendingreflective layer (104) and reflective layer (103). Part of the substrateis etched away to allow the passage of incident reference light orincident infrared light. The reflective layer (103) can be on the lowersurface of the substrate (101), or suspended above the lower surface ofthe substrate (101) through a supporting structure. Similar to theprinciple illustrated above, as infrared light is incident from the sameside as the reflective layer (103), reflective layer (103) absorbs moreheat than the suspending reflective layer (104), causing the gap betweensuspending reflective layer (104) and reflective layer (103) to change,as well as the resonant wavelength of the FP interferometer formed bysuspending reflective layer (104), reflective layer (103) and the gap.As a result, the intensities of the transmitted or reflected referencelight of the FP interferometer change, and the intensity of thetransmitted or reflected reference light (109) changes subsequently.

The configuration in FIG. 1F is similar to FIG. 1E, and the differenceis that the reflective layer (103) is directly attached to the lowersurface of the substrate (101) and is largely transparent to infraredlight. When the infrared light is incident from the same side as layer(103), more light is absorbed by suspending reflective layer (104) thanby reflective layer (103), causing the gap to change. The basic workingprinciple of the infrared sensor in FIG. 1F is similar to that in FIG.1E, and will not be repeated. Furthermore, the infrared sensor inaccordance to this invention can have different configurations. Forexample, the reflective layer in FIG. 1F is above the suspendingreflective layer, where the reflective layer transmits more infraredlight and the suspending reflective layer absorbs more infrared light.The interference change upon the absorption of incident infrared lightcauses change in the intensity of reference light. Furthermore, thesupporting mechanism of the suspending reflective layer can be attachedto the substrate, or the reflective layer, or the supporting mechanismof the reflective layer, as long as it keeps the suspending reflectivelayer suspended. Furthermore, the substrate can be selected to havevarious functions. For example, the substrate can be CMOS or CCD imagercircuits or wafers. Furthermore, besides the infrared sensors of thisinvention, the substrate can have other circuits or devices, such asimaging circuits, control circuits, etc.

FIG. 1G shows the spectra of an infrared sensor and a reference light inaccordance to one embodiment of the invention. Curve (121) is thetransmission spectrum of infrared sensor when there is no incidentinfrared light. When infrared light is incident on the sensor, thetemperature of the suspending reflective layer (104) changes forabsorbing infrared light, the suspending reflective layer (104) and thebeam (106) expands, causing the suspending reflective layer (104) tomove vertically. The gap between the suspending reflective layer (104)and the reflective layer (103) changes, resulting in the new spectrum asshown by curve (122). In addition to the change in resonant wavelength,the shape of the spectrum may also change. The spectrum of the referencelight is shown by curve (123). When there is no incident infrared light,the intensity of the transmitted reference light is the intensity of thereference light multiplied by the transmitivity of the sensor,illustrated by the overlapped area (124) of the two curves. When thereis incident infrared light, the intensity of the transmitted referencelight is increased, the increased intensity is illustrated by the area(125).

Therefore, using MEMS fabrication techniques, a FP interferometer iscreated by the suspending reflective layer (104), the reflective layer(103), and the air or vacuum gap between the two layers. The FPinterferometer also comprises a beam (106) that is made by differentmaterials. When infrared light (108) is incident, the temperature of thesuspending reflective layer (104) and the beam (106) changes, causingthe gap between the two layers to change. The gap change shifts theresonant wavelength of the FP interferometer, causing the transmissionof the reference light (102) to change. The infrared sensor inaccordance to this invention is sensitive, has fast response time, iseasy to fabricate, has good uniformity, and uses simple imaging system.

Based on the principle of resonance in a FP interferometer, thetransmission or reflection of the reference light is very sensitive tothe change of the gap distance. When less sensitivity is desired, thereflective films can be designed so that the interferometer has abroader spectrum. The intensity of transmission or reflection of thereference light is therefore less sensitive to the gap change. Morebroadly, the sensor can be constructed not as a strict FPinterferometer, as long as the gap change results in the change oftransmission or reflection of the reference light. For example, in FIG.1H, the reflective layer and the suspending reflective layer of theinfrared sensor in accordance to another embodiment of the invention aredesigned as the following: the substrate is a glass wafer, the lowerreflective layer is a 200 nm a-Si layer. The suspending reflective layeris constructed, from top to bottom, as 50 nm a-Si/100 nm MgF2/400 nmSiN. The gap is 1200 nm. In this structure, neither the reflective layernor the suspending reflective layer is a strict Bragg reflector. Thesimulated transmission curve of this structure is shown in FIG. 1H. Thisfigure is for illustrative purpose only. The actual transmission curvemay be different due to different materials or parameters. The simulatedresult shows that the spectrum of this structure changes as the gapchanges. In this structure, the reference light can be selected to havea wavelength near the dashed lines in FIG. 1H. Around theseswavelengths, the transmission or reflection of the reference lightchanges as the gap changes, and therefore can be used as an infraredsensor in accordance with this invention.

In another embodiment, the infrared sensor can be adapted to detectother light at different wavelengths, such as ultraviolet light. Forexample, the suspending reflective layer absorbs light at certainwavelength, but not the reference light. On the other hand, thesuspending reflective layer, the reflective layer, and the gap form aninterferometer that transmits or reflects the reference light. Thesensor is then a sensor for that wavelength. Preferably, the said lightat certain wavelength is ultraviolet. Therefore, materials or number oflayers can be selected to construct the suspending reflective layer orthe reflective layer so that the suspending reflective layer absorbslight at certain wavelength, and the sensor then detects light at thatcertain wavelength. The materials and number of layers can also beselected to construct the suspending reflective layer and reflectivelayer not to be strict Bragg reflectors. The sensor can also detectlight at the certain wavelength. Such variations are within the scope ofthis invention.

The infrared sensor in this embodiment has a suspending reflective layer(204) that is supported by beam (206). The beam is designed so that thesuspending reflective layer (204) moves vertically and in parallel tothe initial position as temperature changes. FIG. 2A-C shows thestructure of a spin-wheel beam (206) in an infrared sensor in accordancewith one embodiment. The spin-wheel beam (206) can rotate around thesuspending reflective layer (204), and is rotationally symmetric. Thebeam (206) has a beam body and an additional layer (210), as shown inFIG. 2A and 2C. The additional layer (210) can be attached to the upperor lower surface of the beam (206). In FIG. 2B, each beam has twoadditional layers (210). Each additional layer can be attached to thesame side of the beam surface, such as the upper or the lower surface.In FIG. 2A-C, the additional layer (210) attached to beam (206) isusually made of metals with high CTE, and has a high conductivity. Toincrease the thermal insulation of beam (206) and therefore increase thetemperature rise of the suspending reflective layer (204) when itabsorbs incident infrared light, the length of beam (206) can beincreased. In the spinwheel structure, part of the beam (206) cancontain no metal so as to increase its thermal resistivity. Since thespinwheel structure has rotational symmetry, the suspending reflectivelayer (204) moves vertically and in parallel as temperature changes. Thesuspending reflective layer (204) can have various shapes, such asrectangle and hexagon.

FIGS. 3A-C show another configuration of the infrared sensor inaccordance with another embodiment of the invention. The sensor has onlyone beam (306). It includes: a substrate (301), a reflective layer(303), a suspending reflective layer (304), a beam (306), and additionallayers (310) and (310′) attached to the beam (306). Part of the metaladditional layer (310) is attached to the upper surface of the beam(306), part of the metal additional layer (310′) is attached to thelower surface, as shown in FIG. 3B. When the temperature changes, thebending angle of the two parts cancel and the suspending reflectivelayer (not shown in the figure) moves in parallel. The advantage of thesingle beam structure is the low thermal conductivity and low stress.The single beam configuration can use a straight beam as shown in FIG.3A, or a reflexed beam as shown in FIG. 3C. The reflexed single beamstructure forms a regular and compact shape as the beam reflexes backand forth at one side of the suspending reflective layer (304).

FIG. 4A shows another configuration in accordance with anotherembodiment of the invention where reflexed beam (406A) forms adiagonally symmetric structure. The beam (406A) can be reflexed multipletimes, and the displacement of each section adds up to increase thedisplacement of the suspending reflective layer. The structure in FIG.4A is also a spinwheel structure, and the beam (406A) is also aspinwheel reflexed beam. FIG. 4B shows a minor symmetric reflexed beam(406B) in accordance with another embodiment of the invention.

In the beam structures described above, the different CTE's of thedifferent materials in the beam cause the bending as temperaturechanges. Another embodiment is a microbridge structure that does notrely on the principle of different CTE's. In the microbridge structure,the thermal expansions of the suspending reflective layer and the beamcreate a vertical displacement of the suspending reflective layer. Thebeam can comprise a single material or a mix of several materials. Noadditional layer is needed. FIGS. 5A-5B show the top view and thecross-section view of a microbridge structure. The beam (506) can bemade with one material, preferably, with low thermal conductivity. Whenthe suspending reflective layer (504) absorbs infrared light and itstemperature rises, the thermal expansion of the suspending reflectivelayer and the beam pushes the suspending reflective layer up or down,creating a change in the gap distance, subsequently causing theintensity of the transmitted or reflected reference light to change,which can be detected to measure the amount of incident infrared light.

The suspending reflective layer in this invention absorbs heat andgenerates a detectable signal as described above. At the same incidentinfrared light intensity, the more it absorbs, the more the temperaturerises, the stronger is the signal. When the infrared light is incidenton the suspending reflective layer, some is reflected, some absorbed togenerate a detectable signal, and the rest transmitted. The transmittedinfrared light reached the substrate and some is absorbed (notgenerating useful signal), some reflected, which may again be partlyabsorbed by the suspending reflective layer, and so on. The morereflected infrared light from the substrate, the more is being absorbedby the suspending reflective layer. FIG. 6 shows another embodiment thatis designed to increase the infrared absorption of the suspendingreflective layer. FIG. 6 shows various positions of a infraredreflective film (607) incorporated to increase the infraredreflectivity. The infrared reflective layer is films made of materialsthat are highly reflective to infrared light, including electricallyconductive materials such as metals, ITO, InZnO and ZnO. The infraredreflective film (607) highly reflects infrared light. Therefore, theinfrared reflective film (607) strongly reflects infrared lighttransmitted through the suspending reflective layer, allowing thesuspending reflective layer to absorb more infrared light.

ITO, i.e., indium tin oxide, is widely used as transparent electrodes inLCD displays. It has the special property of being both transparent andelectrically conductive. Other materials that have such property includeindium zinc oxide (InZnO) and zinc oxide (ZnO). Therefore, the infraredreflective film (607) is preferably made of ITO, InZnO, or ZnO. Thesematerials are highly reflective to infrared light because of theelectrical conductivity. Therefore, transparent and conductive materialssuch as ITO can be deposited to the substrate to increase the absorptionof infrared light by the suspending reflective layer. The transparentconductive materials such as ITO, when used to form infrared reflectivefilm (607), can be directly coated on the substrate (601), or as onelayer or more layers in the reflective layer (603), or on the uppersurface or lower surface of the reflective layer (603), as shown in FIG.6. When the infrared sensor operates at reflectance mode, the referencelight is not required to transmit through the reflective layer (603) orthe substrate (601). Therefore, opaque materials, such as metals, can beused in the reflective layer (603) or as the substrate (601).

In the above configurations, the structure moves as the temperaturechanges and generates signals. The temperature change of the structureis due to the absorption of incident infrared light, or due toenvironment temperature change around the sensor itself. Infraredsensors based on MEMS structures may not be able to differentiatebetween the two. For example, the bimorph structures bend when incidentinfrared light is absorbed. On the other hand, the temperature change ofthe sensor environment creates bending as well. If the bending due todifferent reasons can not be differentiated, false infrared image iscreated. To prevent the false infrared image, the infrared sensor pixelscan be controlled at a precise temperature, which is difficult. Or, asensor can be designed to respond only to incident infrared light, butnot the temperature change of the environment. In order to create sucheffect, the environment temperature effect needs to be compensated, sothat the sensor only responds to incident infrared light. FIG. 7A-7Cshows a configuration of this concept in accordance with one embodimentof the invention.

FIG. 7A illustrates the temperature compensation method of oneembodiment. The beam comprises three sections: a first section that isclose to the substrate, with an additional layer; a second section thatis close to the suspending reflective layer, with an additional layer;and a third section that is between the above two sections, used forthermal insulation. When environment temperature changes, thedisplacements of the first and second sections cancel each other,causing no displacement of the suspending reflective layer. FIG. 7Bshows an example where the beam is straight. The materials of theadditional layers can be different. For example, the material of theupper additional layer is different from that of the lower additionallayer. The dashed lines in FIG. 7A and 7B illustrate the bending of thebeams when environment temperature changes. In an ideal situation, theend of the beam does not move when the bending of each section cancels.When infrared light is incident and absorbed, the temperature gradientbetween the suspending reflective layer and the substrate causes thebeam end to move, as the displacement in each section does not canceleach other.

Another example is illustrated in FIG. 7C. The beam comprises threesections: a first section that is close to the substrate, containing anadditional layer (710); a second section that is close to the suspendingreflective layer (704), containing an additional layer (711); and athird section between the first and second sections, without anyadditional layer, as the thermal insulator. When environment temperaturechanges, the displacements of the first section and the second sectioncancel each other, causing no displacement of the suspending reflectivelayer (704). When infrared light is incident on the suspendingreflective layer, however, a temperature gradient is created from thesuspending reflective layer (704) and the substrate. The second section,which is close to the suspending reflective layer (704), has atemperature that is close to that of the suspending reflective layer(704) and causes a displacement. The first section, which is close tothe substrate, has a temperature that is close to the substrate, andcreated little or no displacement. The displacements of these twosections thus do not cancel each other. As a result, the suspendingreflective layer moves, generating signals.

To make the first section and the second section move in oppositedirections, the additional layers (710) and (711) are arranged inopposite: the additional layer (710) includes a first additional layer(710′) and a second additional layer (710″), the additional layer (711)includes a third additional layer (711′) and a fourth additional layer(711″). The additional layer in (710) that is close to the additionallayer in (711) are attached to the same side, i.e., the secondadditional layer (710″) of (710) is at the same side with the thirdadditional layer (711′), e.g., the lower surface of the beam. Theadditional layer in (710) that is farther from the additional layer in(711) is attached to another side, i.e., the first additional layer(710′) in (710) is at the same side as the fourth additional layer(711″) in (711), e.g., the upper surface of the beam. This arrangementcreates a temperature compensation mechanism. The number of saidadditional layers can be chosen as needed, as long as the section closeto the suspending reflective layer (704) has a displacement that cancelsthat of the section close to the substrate (701) as environmenttemperature changes.

Another embodiment is to use double suspending layer to implementtemperature compensation. FIG. 8 shows a double suspending layerstructure used for temperature compensation in accordance with oneembodiment of the invention. In this configuration, the lower reflectivelayer is also suspended, similarly supported by a beam as shown in FIG.1A. The first suspending reflective layer (804), the second suspendingreflective layer (806), and the gap between them form an interferometer,wherein the first suspending reflective layer (804) is supported by thebeam (810) which is attached to the substrate. The second suspendingreflective layer (806) is supported by beam (811) which is attached tothe substrate. When environment temperature changes, both suspendingreflective layer moves by the same amount, keeping the gap unchanged.When infrared light is incident, the first suspending reflective layer(804) absorbs more than the second suspending reflective layer (806).The displacements of the two layers are different, and the gap changesso as to generating a signal. Therefore, this structure is insensitiveto environment temperature change but is sensitive to incident infraredlight. Thus, temperature compensation is realized.

In this structure, to further differentiate the absorption of the firstsuspending reflective layer (804) and the second suspending reflectivelayer (806), a metal or transparent conductive layer such as ITO can beinserted into the second suspending reflective layer (806) to increasethe infrared reflectivity. It increases the absorption by the firstsuspending reflective layer (804) and substantially decreases theabsorption by the second suspending reflective layer (806) (even toalmost zero). FIG. 8 is for illustrative purposes only. In practice, thebeam length of the first suspending reflective layer (804) and thesecond reflective layer (806) can be selected as needed. Preferably, thebeam length of the first suspending reflective layer (804) and thesecond suspending reflective layer (806) are designed to be the same andhave the same structure. However, different lengths or structures canalso be selected based on actual needs.

Another method in accordance with one embodiment of the invention toimplement temperature compensation is to use blind pixels. Whentemperature compensation is not used in the infrared sensor, ortemperature compensation is not perfect, the false image can still becalculated if the environment temperature of the sensor is known, andthe infrared image can be recovered by removing the false image. Todetect the environment temperature of the infrared sensors, blind pixelscan be inserted to the sensor array. A blind pixel in accordance with anembodiment of the invention is a structure that is insensitive or notvery sensitive to incident infrared light, but very sensitive toenvironment temperature. The environment temperature of the infraredsensors can be measured by using the characteristics of the blindpixels. An infrared sensor array may have an uneven temperature profileacross the array. An array of blind pixels can be inserted to theinfrared sensor array, e.g., one blind pixel in every 10×10 infraredsensor pixels. By measuring the temperature of each blind pixel, thetemperature distribution of the infrared sensor array can be calculated.

In this configuration, only one percent of the pixels are blind pixels.The infrared image in the blind pixels can be interpolated fromsurrounding infrared sensors. Blind pixels are only sensitive to itsenvironment temperature, not to the incident infrared light. FIG. 9Ashows a blind pixel that comprises: a substrate (901), a reflectivelayer (904), a reflective layer (903) that is attached to the substrate(901), medium that is between the reflective layers (903, 904). Thereflective layers (903, 904) and medium (905) forms an interferometer.When environment temperature changes, the refractive index of the mediumchanges, shifting the spectrum of the interferometer and causing theintensity of transmitted or reflected reference light to change. Theenvironment temperature can then be measured. When infrared light isincident, the temperature of the blind pixel does not change due to itsgood thermal contact to the substrate, and therefore not sensitive toincident infrared light.

FIG. 9B shows another configuration of the blind pixel. By establishinggood thermal contact between the suspending reflective layer (904) andthe substrate, or making the suspending reflective layer not absorbinfrared light, the incident infrared light does not heat up the blindpixel. The structure is similar to the infrared sensors described inthis invention, and the difference is that the thermal conductivity ofthe beam (906) is increased so that the incident infrared light does notheat up the suspending reflective layer to generate a signal. Toincrease the thermal conductivity, the beam width, thickness,cross-section area or the number of beams is increased. Or materialswith high thermal conductivity, such as metals, are used in the beam.The beam (906) can comprise two layers of metals to increase response toenvironment temperature change. When the environment temperaturechanges, it causes changes in the gap distance and the intensity of thetransmitted or reflected reference light from the first film structureand the second film structure. Thus, the environment temperature can bemeasured by detecting the intensity of the transmitted or reflectedreference light from the first film structure and the second filmstructure. In another example as shown in FIG. 9C, the suspendingreflective layer (904) has an infrared reflective film (907), such asITO. The incident infrared light is reflected and not absorbed by thesuspending reflective layer, its temperature does not change and nosignal is generated. In FIG. 9C, the infrared reflective film can alsobe at the lower surface, or somewhere in the middle, of the suspendingreflective layer (904). To simplify the figure, the reflective layer andthe beam are not shown.

The infrared reflective film can also be incorporated into the blindpixels shown in FIGS. 9A-9C and any other blind pixels so that they donot absorb incident infrared light.

In the embodiments of the invention described above, the additionallayer can be an independent part attached to the beam, or being part ofthe beam.

The infrared sensors described above can be arranged to form an array,i.e., focal plane array (FPA). The infrared sensor can be any sensor inaccordance with embodiments of this invention. Alternatively, the FPAcan also incorporate any of the infrared sensor and blind pixels inaccordance with embodiments of the invention. The FPA comprising any ofthe infrared sensors or comprising any of the infrared sensors and theblind pixels can be used in an infrared imaging system. The infraredimaging system in accordance with this invention includes a referencelight source, a FPA in accordance with this invention, and a detectorthat detects the intensity of the readout reference light. In theinfrared imaging system in accordance with this invention, when theinfrared sensors absorb infrared light, the transmitted or reflectedreference light out of the FPA changes and is detected by the detectorto form an image, and the infrared light is easily measured.

The material combination in accordance with this invention refers to amix of materials, or separate layers of different materials. The beamand additional layer in accordance with this invention can containdifferent materials or layers of different materials. The CTE of thesematerials can be different. In such instances, the beam consisting ofdifferent materials or layers of different materials is considered asone integrated beam with a CTE of its own, and is referred as a materialcombination with a first CTE. The additional layer consisting ofdifferent materials or layers of different materials is treated as oneintegrated layer, and is also referred as a material combination with asecond CTE.

The additional layer in this invention is more broadly defined infunctional terms as a structure whose displacement and the displacementof other layers cause the displacement of the supporting structure whentemperature changes. Therefore, the additional layer in accordance withthis invention can be any layer that is attached to the beam. Or, if thebeam has two or more layers, any of the layers can be considered as anadditional layer, and the rest considered as a whole, namely the beamitself.

The figures illustrate the principle of infrared sensor in accordancewith the invention that utilizes the transmission of a reference light.This invention can also use the reflected reference light to detect theincident infrared light. The basic principle of reflection mode issimilar to the transmission mode. The difference is that reflectedreference light is used to detect the change in the pixel instead of thetransmitted reference light. The basic principle of the reflection modelis not described here so as not to obscure this invention.

Different embodiments of this invention have been described, but thescope of the invention is not to be limited by these exemplaryembodiments. For instance, the beam can be different than thosedisclosed in the exemplary embodiments, and its shape, thickness, andlengths can be selected based on the needs of specific implementations.The shapes of the suspending reflective layer or the reflective layer,the number of layers or types of materials in the suspending reflectivelayer or the reflective layer can be selected based on the needs ofspecific implementations, and can be different from those in theseexemplary embodiments. People in this field might think of or makevarious modification or additions that are still within the scope ofthis invention. This invention is not limited by the exemplaryembodiments disclosed, but includes all modifications, combinations, orreplacements that are within the scope of the claims. The preferredembodiments of this invention are disclosed for the purpose ofillustration this invention, not for limiting this invention.

1. An infrared sensor for detecting infrared light, comprising: areference light source; a first film structure; a second film structure;a gap between said first film structure and said second film structure;a first supporting mechanism for supporting said first film structure ona substrate; wherein said first film structure, said second filmstructure, said gap form an interferometer; and wherein the intensity ofa portion of a reference light generated by said reference light sourcechanges when an infrared light is incident upon said infrared sensor. 2.The infrared sensor of claim 1, wherein said second film structure isdirectly attached to said substrate.
 3. The infrared sensor of claim 1,wherein said first supporting mechanism comprises a beam having a firstend connected to said first film structure, and a second end connectedto at least one of said substrate and said second film structure.
 4. Theinfrared sensor of claim 3, wherein said beam comprises a first materialcomprising a first coefficient of thermal expansion (CTE), and a secondmaterial comprising a second CTE, wherein said first CTE is differentfrom said second CTE.
 5. The infrared sensor of claim 4, wherein saidsecond material comprises a CTE larger than that of the first materialby 50% and is configured as a layer of material attached to the firstmaterial of the beam.
 6. The infrared sensor of claim 1, wherein part ofsaid substrate is etched away to allow the passage of reference light.7. The infrared sensor of claim 1, further comprises a second supportingmechanism for supporting said second film structure on said substrate.8. The infrared sensor of claim 1, wherein said first film structurecomprises an infrared absorptive film.
 9. The infrared sensor of claim1, wherein said second film structure comprises an infrared reflectivefilm.
 10. The infrared sensor of claim 1, wherein said infraredreflective film is transparent to said reference light and electricallyconductive.
 11. The infrared sensor of claim 1, wherein said firstsupporting mechanism comprises a microbridge having at least twomirrorly symmetric and straight beams supporting said first filmstructure.
 12. The infrared sensor of claim 1, wherein said first filmstructure comprises at least two layers of material, wherein said layersof material are symmetrically arranged.
 13. The infrared sensor of claim1, wherein said first film structure comprises a layer of materialselected from a group consisting of: silicon oxide (SiO₂), siliconnitride (SiNx) and amorphous silicon (a-Si).
 14. The infrared sensor ofclaim 1, wherein said first film structure comprises a five layersymmetric structure selected from a group consisting of:a-Si/SiO₂/a-Si/SiO₂/a-Si and SiNx/SiO₂/a-Si/SiO₂/SiNx.
 15. The infraredsensor of claim 1, wherein said first film structure comprises a layerof material having a thickness of a quarter wavelength of the referencelight in the material.
 16. The infrared sensor of claim 1, wherein saidsecond film structure is part of said substrate.
 17. The infrared sensorof claim 1, wherein said substrate is highly reflective to infraredlight.
 18. The infrared sensor of claim 1, wherein said substratecomprises a material selected from indium tin oxide (ITO), zinc oxide(ZnO), indium zinc oxide (InZnO).
 19. The infrared sensor of claim 1,wherein said second film structure comprises a material selected fromITO, ZnO, InZnO.
 20. The infrared sensor of claim 1, wherein said firstfilm structure absorbs at least one of ultraviolet light and milliwavelight.
 21. The infrared sensor of claim 1, wherein said substratecomprises a CMOS circuit or a CCD circuit.
 22. The infrared sensor ofclaim 1, wherein said the gaps changes due to the thermal expansion ofsaid first supporting mechanism when an infrared light is incident uponsaid infrared sensor.
 23. The infrared sensor of claim 1, wherein saidportion of said reference light is transmitted through said substrate.24. The infrared sensor of claim 1, wherein said portion of saidreference light is reflected from said substrate.
 25. An infrared sensorfor detecting infrared light, comprising: a reference light source; afirst film structure; a second film structure comprising a materialselected from indium tin oxide (ITO), zinc oxide (ZnO), indium zincoxide (InZnO); a gap between said first film structure and said secondfilm structure; a substrate; a first supporting mechanism for supportingsaid first film structure on said substrate; wherein said first filmstructure, said second film structure, and said gap form aninterferometer; and wherein the intensity of a portion of a referencelight generated by said reference light source changes when an infraredlight is incident upon said infrared sensor.
 26. An infrared sensor fordetecting infrared light, comprising: a reference light source; a firstfilm structure comprising an infrared absorptive film; a second filmstructure; a gap between said first film structure and said second filmstructure; a first supporting mechanism for supporting said first filmstructure on a substrate; wherein said first film structure, said secondfilm structure, said gap form an interferometer; wherein the intensityof a portion of a reference light generated by said reference lightsource changes as said gap changes due to the thermal expansion of saidfirst supporting mechanism when an infrared light is incident upon saidinfrared sensor.
 27. The infrared sensor of claim 26, wherein saidportion of said reference light is transmitted through said substrate.28. The infrared sensor of claim 26, wherein said portion of saidreference light is reflected from said substrate.
 29. The infraredsensor of claim 26, wherein said first supporting mechanism is arrangedin such a way so that said gap between said first film structure andsaid second film structure does not change when the environmenttemperature of the infrared sensor changes.
 30. The infrared sensor ofclaim 26, further comprises a second supporting mechanism for supportingsaid second film structure on said substrate, wherein said firstsupporting mechanism and said second supporting mechanism are arrangedin such a way so that said gap between said first film structure andsaid second film structure does not change when the environmenttemperature of the infrared sensor changes.
 31. The infrared sensor ofclaim 26, wherein said first supporting mechanism comprises a beamhaving a first section connected to said first film structure and asecond section connected to at least one of said substrate and saidsecond film structure, and a plurality of additional layers attached tosaid beam.
 32. The infrared sensor of claim 31, wherein said firstsection is symmetrically arranged with said second section.
 33. Theinfrared of claim 31, wherein said beam comprises a first materialcomprising a first coefficient of thermal expansion (CTE), and saidplurality of additional layers comprises a second material comprising asecond CTE, wherein said first CTE is different from said second CTE.34. The infrared sensor of claim 31, wherein said second materialcomprises a CTE larger than that of the first material by 50% and isconfigured as a layer of material attached to the first material of thebeam.
 35. The infrared sensor of claim 31, where said plurality ofadditional layers are arranged so that when the environment temperatureof the infrared light sensor changes, said gap does not change due tothe thermal expansion of said first supporting mechanism.
 36. Theinfrared sensor of claim 31, wherein said first section of said beam hasgood thermal contact with said first film structure, said second sectionof said beam has good thermal contact with at least one of saidsubstrate and said second film structure, and said beam furthercomprises a thermally insulating section between said first end and saidsecond end.
 37. The infrared sensor of claim 31, wherein said firstsection and said second section of said beam moves in oppositedirections when the environment temperature of the infrared sensorchanges.
 38. The infrared sensor of claim 31, wherein said first sectionand said second section of said beam moves in directions that minimizethe change in said gap when the environment temperature of the infraredsensor changes.
 39. An infrared imaging system that comprises: areference light source; a detector for detecting the reference lightintensity; and a focal plane array comprising an infrared sensor fordetecting infrared light, the infrared sense comprising a first filmstructure; a second film structure; a gap between said first filmstructure and said second film structure; a first supporting mechanismfor supporting said first film structure on a substrate or said secondfilm structure; wherein said first film structure, said second filmstructure, said gap form an interferometer; wherein the intensity of aportion of a reference light generated by said reference light sourcechanges when an infrared light is incident upon said infrared sensor.40. An infrared imaging system of claim 39, wherein the focal planearray further comprises a blind pixel for detecting environmenttemperature.
 41. An infrared imaging system of claim 40, wherein theintensity of said reference light transmitted through said blind pixeldoes not change when infrared light is incident upon said blind pixel.42. An infrared imaging system of claim 40, wherein the intensity ofsaid reference light transmitted through said blind pixel changes whenenvironment temperature changes.
 43. An infrared imaging system of claim40, wherein said blind pixel does not absorb incident infrared light.44. The infrared imaging system in claim 40, wherein said blind pixelhas good thermal contact with said substrate.
 45. The infrared imagingsystem in claim 39, wherein the reference light source is a lightemitting diode.
 46. The infrared imaging system of claim 39, whereinsaid detector is a CCD or CMOS imaging sensor.